1. Field of the Invention
The present invention relates to a storage system, a storage system control method, and a storage controller. In particular, this invention is suited for use for a storage system having a storage controller.
2. Description of Related Art
These days in storage systems that deal with data on a large-scale, it is necessary to extend the functionality of the storage system itself and increase the number of logical volumes (hereinafter referred to as “logical volumes”) formed in physical storage areas provided by multiple hard disk devices arranged in arrays, in order to store massive amounts of data that increase from day to day in the multiple hard disk devices. Accordingly, the amount of control information for controlling the storage system has also increased. It has therefore become necessary to take measures to increase the capacity of the shared memory required to store the control information.
However, if the power for a storage system that has a backup function stops, the control information stored in the shared memory will be lost after a certain period of time has elapsed. In order to prevent such loss of control information, the control information is stored, not in the shared memory, but in nonvolatile semiconductor memory or hard disk drives mounted on a service processor.
JP-A-2005-196673 discloses a technique for storing operation information, such as operation rates and operation times for a storage system, on multiple hard disk drives configured to be operated according to RAID (Redundant Array of Independent/Inexpensive Disks) methodology. Also, JP-A-2005-258918 discloses a technique for hierarchizing cache memory in a storage system and storing host data from a host computer in the cache memory.
It is necessary to increase the capacity of the shared memory in order to extend the functionality of the storage system itself or to increase the number of logical volumes. However, there is the problem of high cost, because shared memory is expensive.
If the control information is stored in semiconductor memory instead of shared memory, the control information will not be lost, but the amount of control information stored in the semiconductor memory will be less than the amount of control information stored in the shared memory. Accordingly, if the same amount of control information as that stored in the shared memory were to be stored in the semiconductor memory, the semiconductor memory itself would be too expensive.
If the control information is stored in hard disk drives mounted on a service processor, instead of in the shared memory, since not many hard disk drives are configured to be operated according to the RAID system, it is difficult to restore the control information stored in the hard disk drives if a failure should occur in the hard disk drives.
Furthermore, if the control information is stored in any storage device other than the shared memory of the storage system, that storage device needs to have access performance equal to or better than the shared memory.